Magnetic recording medium diskettes, or disks having hubs, generally consist of three elements: an annular recording medium disk, a flanged metal hub, and an adhesive that secures the medium to the flange of the hub. The recording medium is made of a flexible magnetic sheet material that has a typical thickness of about 0.075 mm. The hubs may be stamped from a metal sheet or molded from a thermoplastic with a magnetic insert. The hub has a center portion and a recessed flange portion. The center portion fits through a central aperture in the medium, with the medium resting on the flange portion. An adhesive in between the medium and flange secures the medium to the flange.
The predominant method for the manufacture of hubbed disks is to a place a two-sided pressure-sensitive ring (A-ring) between the medium and hub to secure the medium to the hub. See, e.g., U.S. Pat. No. 4,445,157. Because both sides of the A-ring are a pressure sensitive adhesive, release liners are typically required on each side of the ring prior to the use of the A-ring. There are processing difficulties inherent in the removal of the release liners prior to use, as well as cost and waste concerns in the use of the release liners.
A-rings are typically stamped from a sheet of pressure sensitive adhesive that has a release liner on each side. The adhesive portion removed to form the annular opening of the A-ring, and the adhesive portion that surrounds the A-ring, are discarded after the A-rings are cut from the sheets. The waste and cost inherent in this manufacturing procedure of A-rings is undesirable.
It is important to have an adhesive bond between the hub and medium that does not shift or creep under conditions of use, such as torque shear. As the density of the information stored on magnetic media increases, and the number of tracks on a disk increases, shear resistance becomes increasingly important. Even very small shifts in the relationship between the hub and media can cause the media to fail in its use in reading or recording data. Accordingly, it is important that the adhesive used to bond the hub to the medium have excellent shear resistance characteristics.